Spinal fixation devices are used in orthopedic surgery to align and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation element, such as a relatively rigid fixation rod or plate that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires, or screws. The fixation elements can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the fixation element holds the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
Spinal rods can be mated to a number of anchoring devices fixed to or engaged with the vertebrae along a segment of the spinal column. Since each vertebra varies in shape and size, a variety of anchoring devices have been developed to facilitate engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screws typically include a threaded shank that is adapted to be threaded into a vertebra, and a head portion having a rod-receiving element. A set screw, a plug, or other fastening elements can be used to lock the fixation element, e.g., a spinal rod, into the rod-receiving head of the pedicle screw. In use, the shank portion of each screw is threaded into a vertebra, and once properly positioned, a rod is seated through the rod-receiving member of each screw and the rod is locked in place by tightening a cap or other closure mechanism to securely interconnect each screw and the fixation rod.
The process of placing a rod within or adjacent to an implanted bone anchor so that they are interconnected is referred to as “reducing” the rod. Rod reduction is typically performed using suitable instruments that can create appropriate forces on the implanted bone anchor and the rod. Furthermore, after the rod is seated in the rod-receiving member and captured in a rod-receiving portion of the head of a bone anchor (e.g., a pedicle screw), a final tightening is typically performed on the screw using fastening instruments, for stabilization of the rod. The tightening of the screw can also be performed for maintenance of a surgical correction.
To complete rod reduction and perform final tightening, surgeons use multiple instruments (e.g., screw drivers and torque wrenches) which often need to be applied in multiple steps. This can be a time-consuming and complicated procedure, particularly when multiple bone anchors are used to fixate a rod and/or when the surgical procedure is performed to correct a complex deformity or injury. Multiple steps that require application of manual force induce fatigue so that surgeon's performance during surgery can decrease, which can compromise the outcome of the surgery. As another drawback of existing approaches, torque created by the instruments during the final tightening can be difficult to control.
Accordingly, there is a need for improved methods and devices for applying a closure device to a spinal anchoring device.